A numerical study on the aerodynamics of express boxcars with different marshalling configurations

To understand the influence of marshalling configurations on train aerodynamic characteristics, four configurations (5-car, 7-car, 9-car, and 11-car) are used to investigate the effect of marshalling configurations on aerodynamic forces, time-averaged slipstream, and flow topology. The reliability of numerical results is first validated by comparing them with wind tunnel test results. The results indicate that the influence of train configuration on the aerodynamic resistance of intermediate boxcars can generally be disregarded, although a slight reduction is observed in the aerodynamic resistance of the trailing boxcar as the marshalling length increases. Therefore, it can be preliminarily concluded that a 5-car configuration effectively captures the essential aerodynamic force characteristics of the locomotive in conjunction with multiple boxcars. Additionally, increasing the marshalling length enhances the intensity and scope of the slipstream but does not affect the peak values of the slipstream. Furthermore, as the train marshalling length increases, there is a noticeable rise in the boundary layer momentum thickness (θ). However, there is a significant decrease in θ near the rear of the train, which becomes more pronounced with longer train configurations. Shorter configurations tend to experience higher turbulence levels for cross-sectional profiles symmetric in the spanwise direction (y = 0 plane).